Theoretical analysis of urban runoff pollutographs: identification of characterization variables and impact

This research presents a novel methodology to determine runoff water retention volumes that allow the design of storage tanks for storm sewer overflows. It is based on the use of the Stormwater Management Model (SWMM) to generate hydrographs and runoff pollutographs of a fictional urban basin. Three pollutants (TS, BOD5 and TN) are simulated for a given set of rains and the values taken by a proposed set of characterization variables for the pollutographs obtained are analysed. Correlation and determination coefficients that exist between the different variables are analysed while also performing a multivariate characterization using PCA and cluster analysis. In the case study presented, using IDF curves of the studied city, a probability of occurrence (Tr) is assigned to the values taken by the proposed characterization variables. To assess the impact and identify the most unfavourable pollutographs within the set of selected rains, impact evaluation variables (IEV’s) are established, based on the proposed characterization variables and by simulating the discharge to a receiving water body (river with initial concentration and constant flow). Finally, a storm sewer overflow is simulated, deriving a maximum flow for purification, and dimensioning retention tanks for different fractions of the total volume of runoff to control the maximum values of a specific IEV impact evaluation variable. Taking a design return period Trssd ≥ 10 years, the results obtained in the study case were 146.50 m3/ha imp for a 100% retention of the total runoff volume and 117.20 m3/ha imp for an 80% retention.本研究提出一种用于确定雨水管网溢流调蓄容积的创新方法，可为雨水调蓄池的设计提供支撑。该方法依托雨水管理模型（Stormwater Management Model, SWMM），生成虚构城市流域的流量过程线与径流污染负荷过程线。针对给定的降雨事件集，研究对总固体（Total Suspended Solids, TS）、五日生化需氧量（Biochemical Oxygen Demand 5-day, BOD5）与总氮（Total Nitrogen, TN）三种污染物开展模拟，并对所获取的污染负荷过程线的拟议特征变量取值进行分析。研究分析了不同变量间的相关系数与决定系数，同时采用主成分分析（Principal Component Analysis, PCA）与聚类分析完成多变量特征表征。在本次案例研究中，基于研究城市的降雨强度-历时-频率（Intensity-Duration-Frequency, IDF）曲线，为拟议特征变量的取值赋予发生概率（Tr）。为评估污染负荷过程线的影响并筛选选定降雨事件集中的最不利工况，基于拟议特征变量，通过模拟污染物向受纳水体（具有初始浓度与恒定流量的河流）的排放过程，构建了影响评估变量（Impact Evaluation Variables, IEVs）。最后，对雨水管网溢流过程进行模拟，得出用于净化处理的最大流量，并针对不同径流总容积占比的调蓄池进行尺寸设计，以管控特定影响评估变量的最大值。当设计重现期Trssd≥10年时，本案例研究结果显示：全额截留总径流量时，调蓄容积为146.50 m³/(ha·imp)；截留80%总径流量时，调蓄容积为117.20 m³/(ha·imp)。